Freeze-drying has been known as one type of processing foods and chemicals. In the freeze-drying, the object disposed in a freeze-drying chamber is cooled to freeze moisture in the object. Then, the frozen moisture is sublimated by decompressing and heating the freeze-drying chamber, and the moisture thus emitted into an atmosphere is collected by a cold trap cooled in advance, whereby the object is dried.
FIG. 5 shows an example of a system which implements the freeze-drying. FIG. 5 is a schematic view showing an overall configuration of a conventional freeze-drying system 100′. In particular, this example shows a system which can implement the freeze-drying with a simple configuration by generating cold by a condensing unit as a single heat source device.
The freeze-drying system 100′ includes: a freeze-drying chamber 2 which includes a pipe shelf 1 on which the object is disposed; a cooling device 3 as the condensing unit which generates the cold; a cold trap 4 which collects the sublimated moisture; and a heat exchange unit 5 in which a first refrigerant flowing in the cooling device 3 and a second refrigerant flowing in the pipe shelf 1 exchange heat. A valve 7a for adjusting a flowrate of the first refrigerant is disposed on a circulation line 6 in which the first refrigerant circulate. A bypass line 8a passing through the heat exchange unit 5 and a bypass line 8b which leads into the cold trap 4 are branched from the circulation line 6. Valves 7b and 7c for adjusting an amount of the first refrigerant flowing in are respectively disposed on the bypass lines 8a and 8b. 
A circulation pump 10 for permitting the circulation of the second refrigerant is disposed on a circulation line 9 in which the second refrigerant circulates.
For example, a refrigerant such as CFC or ammonia may be used as the first refrigerant, and anti-freezing solution or oil may be used as the second refrigerant.
A controller 11, as a control unit, implements an operation of the freeze-drying system 100′. More specifically, an open-close state of the valves 7a to 7c, an amount of generated cold in the cooling device 3, and an operation state of the circulation pump 10 are controlled based on a control signal transmitted from the controller 11.
First of all, in the freeze-drying system 100′, the valves 7a and 7b are set to be in the opened state so that the first refrigerant, including the cold from the cooling device 3, is guided to the heat exchange unit 5, whereby the second refrigerant flowing in the pipe shelf 1 is cooled. Thus, the object, disposed on the pipe shelf 1, receives the cold from the second refrigerant to be frozen.
When the object is thus frozen, the cold trap 4 may be cooled at the same time by setting the valve 7c to be in the opened state.
Once the freezing of the object is completed, the freeze-drying chamber 2, including the object, is decompressed by an unillustrated decompressing unit (such as a vacuum pump), whereby the frozen moisture in the object is sublimated. Here, the sublimation of the moisture may be facilitated by heating the second refrigerant with a heating unit such as a heater, in addition to the decompression with the decompressing unit.
The moisture emitted into the atmosphere by the sublimation in the freeze-drying chamber 2 is collected by the cold trap 4 coupled to the freeze-drying chamber 2. The moisture accumulated in the cold trap 4 is discharged to the outside when the freeze-drying is completed.
For example, Patent Document 1 discloses a system of performing freeze-drying by using the cold generated in the cooling device 3 through a plurality of refrigerants. In Patent Document 1, the system configuration is simplified in such a manner that a single cooling device can further cover the cooling of a condenser in the system.
Generally, the freeze-drying needs to cool the object to an extremely low temperature, and thus requires a long freezing period. Thus, higher productivity has been called for. To achieve this, Patent Document 2 discloses a technique of directly supplying an extremely low temperature fluid such as liquid nitrogen into the freeze-drying chamber, in addition to the cooing by the cooling device, to facilitate the cooling to thereby shorten the freezing period.